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<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>

<body>
    <script>
        let PI = 3.14
        let radius = prompt('请输入半径')
        let area = PI * radius * radius
        let age = 18
        document.write(area + '</br>')
        document.write('我今年' + age + '岁了')
    </script>
</body>

</html>